Doppler-effect ground speed sensor for use with a brake system

Abstract

Vehicle anti-lock brake control apparatus having wheel speed sensor for detecting actual speed of a vehicle wheel, solenoid-operated valve for regulating the wheel braking pressure, and controller for controlling the valve, on the basis of the detected actual speed, and vehicle ground-speed detected by ground-speed sensor. The controller controls the valve at a controlled duty cycle, which is determined on the basis of at least a wheel speed error and a time derivative of this error. The error is obtained as a deviation of the detected actual wheel speed from a target wheel speed obtained on the basis of the detected vehicle ground-speed.

What is claimed is: 
     
       1. A Doppler-effect type ground-speed sensor including a transmitter attached to a body of the vehicle and transmitting a wave toward a road surface in a predetermined direction of propagation, a receiver attached to said body and receiving a portion of said wave which is irregularly reflected by said road surface, and a signal processor which provides an output representative of said ground-speed of the vehicle, on the basis of frequencies of said wave transmitted by said transmitter and said portion received by said receiver, wherein the improvement comprises: said receiver is spaced apart from said transmitter by a predetermined distance in one of opposite running directions of the vehicle in which said predetermined direction of propagation is inclined with respect to a direction perpendicular to the running directions.   
     
     
       2. The Doppler-effect type ground-speed sensor according to claim 1, wherein said transmitter generates a ultrasonic wave. 
     
     
       3. The Doppler-effect type ground-speed sensor according to claim 1, wherein said direction of propagation of said wave transmitted by said transmitter is inclined in a forward running direction of the vehicle as said one of opposite running directions, said receiver being spaced apart from said transmitter in said forward running direction. 
     
     
       4. The Doppler-effect type ground-speed sensor according to claim 1, wherein said direction of propagation of said wave transmitted by said transmitter is inclined in a backward running direction of the vehicle as said one of opposite running directions, and said receiver being spaced apart from said transmitter in said backward running direction. 
     
     
       5. The Doppler-effect type ground-speed sensor according to claim 1, wherein said predetermined distance is a function of a selected vehicle speed. 
     
     
       6. The Doppler-effect type ground-speed sensor according to claim 1, wherein said predetermined distance is equal to the distance moved by said vehicle at a selected vehicle speed while said wave transmitted by said transmitter is reflected by said road surface and said portion is received by said receiver. 
     
     
       7. The Doppler-effect type ground-speed sensor according to claim 4, wherein said receiver has an optical axis parallel to an optical axis of said transmitter which is parallel to said direction of propagation.